A servo motor is one example of a motor having a salient pole wound stator. Usually, the stator poles, known as teeth because of their appearance, extend radially with a radially inner surface forming the pole face which is a discontinuous cylindrical surface, which confronts the rotor across a small air gap. The servo motor is commonly used with an electronic controller to provide angular displacement or angular speed in response to control signals. The servo motor has the advantage of having a small volume and light weight, high output power and torque, and being easy to control.
FIG. 1 is a plan view of a laminated stator core of a typical servo motor. The stator core is formed by stacking together a plurality of stator laminations. The stator laminations each comprise a round yoke 1 and a plurality of teeth 3 being uniformly distributed and extending radially inward from the yoke 1. A stator winding (not shown in the figure) is wound around the teeth 3. In the above described stator, the material between the yoke 1 and teeth 3 can not be used, so the material utilization ratio is low. While winding the wires of the winding about the teeth, the winding tool needs to be shuttled continuously at the gap 5 between yoke 1 and teeth 3, and because of the limitation of the gap 5, the winding is very inconvenient and time-consuming. Further more, a comparative big gap must be left between the windings wound on two adjacent teeth 3, so as to let the winding tool to pass through the gap. The comparatively big gaps provided between the windings limit the slot coil ratio of the windings, thus the efficiency of the motor will be less than maximum. To allow the winding tool pass through, a comparatively big clearance 7 must also be provided between the ends of two adjacent teeth 3; however, the bigger the clearances 7, the bigger the fluctuation in the motor torque (cogging torque).
To overcome the disadvantages of the above mentioned stator lamination structure, it has been proposed to use split type stator laminations, such as the stator laminations formed from T-shape lamination units disclosed in U.S. Pat. No. 5,729,072. However, the stator core produced by such T-shape lamination units still has disadvantages of inconvenient winding methods, low material utilization ratio, etc.